I'm kind of eyeballing it with a ruler, but it looks like the 7 or so inches closest to the gun of my 14" are 7/8", and the end steps out to 15/16".

**Edit**
Thought it worth mentioning that the spyder J&J is smaller outside diameter than other threads. Some of my friends have the A5 thread and it starts much larger. I think I read somewhere that it was reduced so it would work with the MR2/MR3 shrouds, which it does.